including decals in weight painting for rigged models
I think that you should be able to make use of 'empty weights' and mesh data transfer to copy the weights from your weight painted body to the separate clothes.
I came across this useful answer that should hopefully be of use to you : https://stackoverflow.com/questions/34719718/transferring-rig-weights-from-one-mesh-to-another-in-blender-2-76/34760742#34760742